1. Field of the Invention
This invention relates to an electronic clinical thermometer and, more particularly, to a predicting-type electronic clinical thermometer for predicting the final temperature at which the thermometer will stabilize, and for displaying the predicted temperature. The invention further relates to a method of measuring body temperature.
2. Description of the Prior Art
With the conventional electronic clinical thermometer of the above-described type, the temperature which will prevail upon thermal stabilization of the electronic clinical thermometer is predicted from measured temperature and is displayed before thermal stabilization is attained. Typically, prediction of temperature is performed by monitoring, over a period of time, the measured temperature as well as the rate of change thereof with time, and employing these two variables along with a function for anticipating temperature in which the variable is the elapsed time up to the moment of observation. The predicted final, stable temperature is uniquely defined by the actual values of these three variables.
With an electronic clinical thermometer that operates by anticipating the final, stable temperature, an advantage is that measurement of temperature is completed before thermal stabilization is attained, thereby reducing the time required for measurement. However, a disadvantage with such a thermometer is that the accuracy with which temperature is predicted declines markedly unless a proper temperature anticipation function is chosen.
Ordinarily, the temperature anticipation function has a temperature rise curve the shape whereof differs depending upon the portion of the body being measured, such as the region under the armpit or the interior of the mouth.
Temperature measurement, namely the operation of predicting what the final temperature will be upon stabilization, is performed by repeating the operation at a series of discrete points in time. The measurement is judged to have ended when the value of the predicted stable temperature exhibits a rate of change within prescribed limits, that is, when the difference between the immediately preceding predicted value and the presently predicted value falls within a prescribed range. When measurement is judged to have ended in this manner, the arithmetic operations for predicting temperature cease and the predicted temperature which should be reached at stabilization is displayed. In general, the display of predicted temperature is retained or "frozen" on the display device until the thermometer power supply is turned off.
Generally, direct reading-type clinical thermometers such as the common mercury thermometer give a temperature reading closer to what the final temperature will be the longer the temperature measurement is performed. Therefore, the accuracy of the measurement rises with the length of the measurement. With the predicting-type electronic clinical thermometer, as described above, the display of the predicted value is frozen on the display device when the measurement is judged to have ended so that, unlike the direct reading thermometer, a more accurate predicted value will not appear on the display even if the length of the measurement is extended. In other words, the conventional predicting-type electronic clinical thermometer can only present a display of predicted stable temperature the accuracy of which is a characteristic of the particular thermometer.
When an electronic clinical thermometer is manufactured or shipped, or during use of the thermometer at a medical facility such as a hospital, it is common practice to perform an inspection for the purpose of calibrating or verifying the absolute precision of the thermometer. However, a predicting-type electronic clinical thermometer presents a problem. Specifically, when an ordinary constant temperature bath is used to test the thermometer, the predicted value displayed is different from the actual temperature of the bath. To avoid this problem, even the electronic clinical thermometer must be so designed as to make a transition to the direct-reading operating mode under special temperature conditions, with the inspection being carried out under these temperature conditions. Alternatively, the electronic clinical thermometer must be provided with a mode changeover switch so as to enable selection of either the predicting or direct-reading operating mode.
As mentioned above, the temperature rise curve, which is for carrying out the arithmetic temperature computations, has a shape which differs depending upon the portion of the body being measured, such as the armpit region or the interior of the mouth. Also, the predicting-type electronic clinical thermometer is adapted to retain the value of the predicted temperature on the display at the conclusion of the measurement computations. Therefore, if the thermometer for measuring temperature orally is used to conduct a measurement in the armpit, the predicted value displayed will not be correct. The same is true if the thermometer for armpit measurement is used for oral measurement.